WoodSense: Royal Paulownia

Royal Paulownia

Paulownia tomentosa is known by a variety of names – Empress tree, Kiri tree, Sapphire Princess, Royal Paulownia, Princess tree, and Kawakami. The most common name, Royal Paulownia, is said to honor Princess Anna Pavlonia (1795-1865), daughter of Russia’s Czar Paul I. Native to China, the tree was first mentioned in an encyclopedia around 1000 B.C. The Chinese cultivated the paulownia tree extensively because of its omen for good fortune. Even today, traditional Chinese medicine uses parts of the tree for many things from darkening graying hair to treating hallucinations. Paulownia made its way to Japan, where it was valued for its light, but strong wood. It had a variety of uses from housing materials to wooden footwear. Japanese custom once held that when a daughter is born, a paulownia tree should be planted. When she marries, the tree is then harvested to build her dowry chest and furniture.

Paulownia has a straight grain, and high strength-to-weight ratio.

Coming to America

In the mid-1800s, paulownia seeds were used as packing material for delicate porcelain shipped from the Orient, and in this way came to the United States. The tree spread relatively unnoticed throughout the country until the 1970s, when Japanese demand for the wood surpassed the supply. Japanese lumber buyers bought every paulownia tree they could find, with anecdotal reports quoting prices as high as $20,000 for a single log.

One of the magical characteristics of the paulownia is its growth rate. With good environmental conditions, the tree can grow as much as 10' in its first year, and reach a diameter of 2' and a height of over 50' in 15 years. At this size, it is ready for harvesting. It grows so fast, that in 1999 the Southeast Exotic Pest Plant Council classified the paulownia trees as an “Invasive Exotic Pest Plant” in Tennessee.

Although mature trees have more normal-sized leaves, young trees are easily recognized by leaves approaching the size of elephant ears. The leaves are high in protein and nutrients, make an excellent fodder for livestock and if mulched into the ground make a good fertilizer.

Paulownia bark is grayish brown with shallow fissures. In mid- to late spring, individual tube-like, 11/2" to 2" long flowers appear that are lavender in color and very fragrant.

Another magical characteristic of paulownia is the high strength of its wood. It has the highest strength-to-weight ratio of any known species. Paulownia wood weighs about 15-19 lbs. per cubic foot, about half the weight of pine and one-third the weight of oak. Also interesting is the wood’s high ignition point of 420 degrees C (788 degrees F). That’s almost twice as high as most domestic hardwood and softwood species.

The leaves of young Paulownia trees are huge, sometimes reaching as much as 3' in diameter.

Inside the Wood

Paulownia sapwood is almost white, while the heartwood runs from purplish-brown to light gray.

The grain is straight with a medium to coarse texture. Another special feature of this wood is its shrinkage values – when dried from green to oven-dry, it shrinks only 2.2 percent across the radial plane and 4 percent across the tangential plane. This makes paulownia very stable during changes in seasonal humidity. Because of these low-shrinkage properties, paulownia doesn’t really need to be kiln-dried and can be ready to work after air-drying for as little as 30 days.

The wood of the paulownia is insect-resistant, and highly resistant to decay under conditions where the lumber isn’t touching the ground. The lumber has good nail- and screw-holding capabilities and machines well, although its high silica content can dull cutting tools rather quickly.

After the buying frenzy of the Japanese, Americans reconceived the value of paulownia and started plantations across the country in the early 1990s. (Former President Jimmy Carter is a big proponent of paulownia lumber.)

The first domestic crops are now being harvested, so you can likely expect to hear a lot more about this magical tree and its lumber.

Born and educated in Germany, Udo Schmidt has written numerous magazine articles and is the author of “Building Kitchen Cabinets.”